Approach to Unexpected Thrombocytopenia
1. INTRODUCTION
Thrombocytopenia คือ platelet count
<150,000/µL ในผู้ใหญ่ และมี clinical spectrum ตั้งแต่ incidental finding →
life-threatening bleeding หรือ thrombosis (เช่น
ITP, HIT, TTP, DIC)
แนวทางประเมินต้องตอบ 4 คำถามหลัก:
1.
Thrombocytopenia จริงหรือไม่ (artifact?)
2.
เป็น acute หรือ
chronic?
3.
isolated หรือมี cytopenia อื่นร่วม?
4.
มีภาวะฉุกเฉินที่ต้องรักษาทันทีหรือไม่
(TTP, HIT, DIC ฯลฯ)
ใช้ได้ทั้งใน primary care, ER, ICU และ hematology consult
2. DEFINITIONS & CLINICAL SIGNIFICANCE
2.1 Severity classification
|
ระดับ |
Platelet count |
|
Mild |
100–149 x10⁹/L |
|
Moderate |
50–99 x10⁹/L |
|
Severe |
<50 x10⁹/L |
|
Very severe (clinical) |
<20–30 x10⁹/L |
ใน ITP มักใช้
<30,000/µL เป็น severe
2.2 Platelet count interpretation (clinical pearl)
- Platelet
count มี narrow range ต่อ “แต่ละบุคคล”
- drop จาก 400k →
200k = clinically significant แม้ยัง >150k
- ต้องดู trend + baseline เสมอ
3. BLEEDING RISK: WHEN TO WORRY
3.1 Platelet count vs bleeding (important concept)
Correlation “weak” →
bleeding risk ขึ้นกับ:
- Platelet
function
- Coagulopathy
- Underlying
disease
- Anticoagulant/antiplatelet
drugs
3.2 Clinical predictors of bleeding (สำคัญกว่า
platelet number)
- Prior
bleeding history
- Wet
purpura (oral/mucosal)
- Hematuria
- Hematologic
malignancy
3.3 Practical bleeding thresholds (clinical guide)
|
Platelet |
Clinical risk |
|
>50k |
surgery usually safe |
|
>100k |
neurosurgery/major surgery |
|
<20k |
↑
spontaneous bleeding |
|
<10k |
high risk life-threatening
bleeding |
Note:
ITP bleeding risk < aplastic anemia at same platelet (young functional
platelets)
4. WHEN TO WORRY ABOUT THROMBOSIS (CRITICAL)
Thrombocytopenia ≠ protection from thrombosis
ต้องคิดถึง:
- HIT
(heparin 5–10 วัน)
- PITT/VITT
(anti-PF4 syndromes)
- APS
- DIC
- TTP/HUS
(TMA)
- PNH
- ITP +
thrombosis (AF, VTE)
5. MAJOR PATHOPHYSIOLOGIC MECHANISMS (High-yield
framework)
5.1 Decreased production (bone marrow failure)
สาเหตุสำคัญ:
- Aplastic
anemia
- MDS /
leukemia
- Bone
marrow infiltration (cancer)
- B12 /
Folate / Copper deficiency
- Severe
infection
- Liver
disease (↓TPO)
- PNH
(BM failure component)
Clue:
- Pancytopenia
- Anemia
+ thrombocytopenia
- Abnormal
smear
5.2 Increased destruction / clearance
Immune-mediated
- Primary
ITP (common)
- Secondary
ITP (SLE, HIV, HCV)
- Drug-induced
immune thrombocytopenia
- Post-transfusion
purpura
Lab pattern:
- Normal
fibrinogen
- Normal
D-dimer
5.3 Consumptive thrombocytopenia (thrombotic/critical)
Life-threatening group:
- DIC
- HIT
- TTP/HUS
(TMA)
- PITT/VITT
Lab clue:
- ↑ D-dimer
- ↓ fibrinogen (DIC)
- Schistocytes
(TMA)
5.4 Redistribution / sequestration
- Splenomegaly
- Cirrhosis
/ portal hypertension
- MASLD
(metabolic dysfunction-associated steatotic liver disease = NAFLD)
Typical platelet: 60–100k (mild–moderate)
5.5 Dilutional
- Massive
transfusion
- Fluid
resuscitation
- Postoperative
(day 2–3)
6. EMERGENCY THROMBOCYTOPENIA (DO NOT MISS)
ต้อง consult hematologist ด่วนถ้าสงสัย:
- TTP
/ HUS / TMA (thrombotic microangiopathy)
- HIT
/ PITT
- Acute
DIC
- Acute
leukemia
- Aplastic
anemia
- HLH
- Severe
bleeding + platelet <50k
- Pregnancy
+ severe thrombocytopenia
7. CLINICAL CONTEXT-BASED DIFFERENTIAL
7.1 ICU / critically ill (common causes)
- Sepsis
(most common)
- DIC
- Drug-induced
- Liver
disease
- Massive
transfusion
- Multicausal
7.2 Postoperative thrombocytopenia
- Nadir:
48–72 hr
- Mechanism:
dilution + consumption
- CPB:
drop up to 50%
7.3 Infection-related thrombocytopenia
Viral
- EBV,
hepatitis C, HIV
- COVID-19
- Dengue,
SFTS (severe fever with thrombocytopenia syndrome) (SE Asia relevance
clinically)
Bacterial/sepsis
- DIC
- marrow
suppression
Parasite
- Malaria,
babesiosis
8. APPROACH TO EVALUATION (Step-by-Step Clinical
Algorithm)
STEP 1: Confirm it is REAL
- Repeat
CBC
- Peripheral
smear review
- Rule
out pseudothrombocytopenia (EDTA clumping)
Key cause:
- EDTA-dependent
platelet clumping (~0.1%)
STEP 2: Assess severity & urgency
- Bleeding?
- Platelet
<50k?
- Thrombosis?
- Acute
illness?
STEP 3: Focused history (high-yield checklist)
Essential history:
- Previous
platelet counts (trend)
- Drug
exposure (last 2 weeks!)
- Heparin
exposure (flush included)
- Transfusion
history
- Infection/travel
(malaria, dengue)
- Alcohol
use
- Autoimmune
disease
- Diet
(B12, folate, zinc excess)
- Family
history (inherited thrombocytopenia)
STEP 4: Physical examination clues
|
Finding |
Suggests |
|
Petechiae/purpura |
platelet disorder |
|
Wet purpura |
severe bleeding risk |
|
Splenomegaly |
hypersplenism/liver disease |
|
Lymphadenopathy |
lymphoma/infection |
|
Neurologic signs |
TTP/TMA |
|
Thrombosis |
HIT, APS, PNH |
9. LABORATORY WORKUP (CORE PANEL)
9.1 Mandatory baseline tests
- CBC
+ smear (critical)
- LFT
+ metabolic panel
- PT/aPTT
- HIV
testing
- HCV
testing
9.2 Peripheral smear key clues
|
Finding |
Diagnosis clue |
|
Schistocytes |
TMA / DIC |
|
Giant platelets |
inherited disorder / ITP |
|
Blasts |
leukemia |
|
Hypersegmented neutrophils |
B12/folate deficiency |
|
Leukoerythroblastic picture |
marrow infiltration |
9.3 Targeted tests (based on suspicion)
- D-dimer,
fibrinogen → DIC
- LDH,
Cr → TMA
- Anti-PF4
Ab → HIT
- ANA
/ APL Ab → autoimmune
- Cultures
→ sepsis
- Bone
marrow biopsy →
unclear etiology / pancytopenia
10. COMMON CLINICAL SCENARIOS
10.1 Isolated thrombocytopenia + normal CBC
Most likely:
- ITP
- Drug-induced
thrombocytopenia
- Viral
infection
- Early
liver disease
10.2 Pancytopenia
Think:
- Aplastic
anemia
- MDS
- Leukemia
- Bone
marrow infiltration
- Severe
infection
- Nutritional
deficiency
10.3 Mild incidental thrombocytopenia (100–149k)
Common causes:
- Normal
variation
- Early
ITP
- Occult
liver disease
- HIV/HCV
- MDS
(long-term risk)
11. DIAGNOSIS OF EXCLUSION (VERY HIGH-YIELD)
11.1 Drug-induced thrombocytopenia
- Onset:
1–2 weeks (new drug)
- Hours
if prior exposure
- Recovery:
5–7 days after stopping drug
Common drugs: - Antibiotics
(vancomycin, rifampin, beta-lactams)
- Antiepileptics
(phenytoin, carbamazepine)
- Heparin
(special: HIT)
11.2 Immune thrombocytopenia (ITP)
Diagnosis when:
- Isolated
thrombocytopenia
- Normal
smear
- No
systemic illness
- Negative
secondary causes
Bone marrow not routinely required
12. GENERAL MANAGEMENT PRINCIPLES (Practical Clinical)
12.1 Treat underlying cause (core principle)
12.2 Platelet transfusion indications
- Active
life-threatening bleeding
- Platelet
<10,000 (prophylaxis)
- Urgent
invasive procedure
- Not
routinely for ITP (unless bleeding)
12.3 Medications & precautions
Avoid:
- NSAIDs
- Aspirin
- Ginkgo
- Antiplatelets
(if not essential)
12.4 Anticoagulation in thrombocytopenia
Key concept:
Thrombocytopenia does NOT protect from thrombosis
- 50k:
anticoagulation usually acceptable if indicated
- <50k:
individualized decision
12.5 Activity restriction
- <50k:
avoid high-impact sports
- Routine
daily activity: usually safe
13. WHEN TO REFER HEMATOLOGY (Strong Indications)
- New
unexplained thrombocytopenia
- Platelet
<50,000
- Suspected
TTP/HIT/DIC
- Pancytopenia
- Abnormal
smear (blasts, schistocytes)
- Need
urgent procedure
- Pregnancy
+ thrombocytopenia
14. KEY CLINICAL PEARLS (Exam + Practice)
- Always
rule out pseudothrombocytopenia first
- Trend
> single platelet value
- Isolated
thrombocytopenia = ITP or drug until proven otherwise
- Schistocytes
+ thrombocytopenia = TMA emergency
- Heparin
exposure + platelet drop >50% = think HIT
- Mild
thrombocytopenia + splenomegaly = hypersplenism
- ICU
thrombocytopenia = sepsis most common
- Platelet
count alone poorly predicts bleeding
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